Grisebach disclosed a damping device for hinges and the like in his U.S. Pat. No. 3,952,365 including a spring for biasing a door or other similar structure into a closed position and a fluid medium for damping movement of the door. The damping effect is achieved by compelling the fluid to pass from one chamber to another within a housing of the device by changing the volumes of the chambers, the spring itself bring used to being about the change in volume.
However such a damping device still has the following drawbacks:
1. In view of a valve flap 33 as shown in FIG. 2 of the Griseback's disclosure, the frequent opening and closing operations of the flap 33 may easily cause fatigue failure to the resilient flap, thereby losing its valve effect and reducing the damping effect of the device.
2. There is not provided with any temporary locking or positioning device for temporarily holding the door at any opening state so that an additional locking or positioning mechanism should be further installed for keeping a temporary door opening state.
3. The pressure-volume worked by the working fluid stored in the cylindrical housing with tiny space is quite limited, thereby causing a very small damping effect.
The present inventor has found the drawbacks of the conventional damping device of a door hinge and invented the present automatic door closer which can be operated by a lighter force.